1. Field of the Invention
The present invention relates to a method of forming devices on a substrate, and more particularly, to a method of forming semiconductor devices of different types on the same substrate.
2. Description of the Related Art
In recent years, optoelectronic integrated circuits are becoming increasingly the center of interest. Monolithic integration of optical devices using gallium arsenide (GAAS) or indium phosphide (InP) and electronic devices using silicon (Si) or GaAs has been expected to cause new functions to be realize and its operation speed to be dramatically increased. Particularly, optical devices are preferably formed two-dimensionally on a substrate to apply the parallel property and spatial propagation property inherent in light to information processing. The Study of such surface emitting devices is disclosed in the "Surface Emitting Semiconductor Lasers" (IEEE Journal of Quantum Electronics, Vol. 24, No.9, pp 1844-1855, September 1988).
However, in order to realize such optoelectronic devices, there are many technical difficulties. When light-emitting elements, light-receiving elements, optical modulators and the like are formed on the same semiconductor wafer, it is difficult to construct all of them suitably by a single growth method and process. In addition, repeating a regrowth process many times is practically impossible for reasons of interface processing.
Then, there has been extensively studied a technique in which materials different in lattice constant, such as Si, GaAs, and InP, are directly grown. Such a technique is disclosed, for example, in the "Growth of GaAs on Si by MOCVD" (Journal of Crystal of Growth, pp 21-26, 68 (1984)). However, since there is the problem that dislocation resulting from a lattice mismatch or a difference in coefficients of thermal expansion is introduced into such a grown film, it is necessary to insert a thick buffer layer.
An effective method for realizing an optoelectronic integrated circuit is to directly bond substrates different in lattice constant. This basic substrate bonding technique is disclosed in the "Si Wafer Direct-Bonding Technique" written by Furukawa at al. (Applied Physics, Vol. 60, No. 8, pp 790-793, 1991). A device manufacturing method using this substrate bonding technique is as follows. Devices are formed on a substrate through a separation layer using an ordinary growth method. The substrate is directly bonded to the other substrate with the devices intervening between them. And then the substrate is separated from the other substrate by selectively etching the separation layer to transfer the devices to the other substrate. Since in this method the number of processes is relatively small and the requirements for the interface are relatively less severe, it becomes possible to bond together respective devices formed optimally on individual substrates or to transfer by means of direct-bonding devices formed optimally on a substrate to another substrate on which an integrated circuit has already been formed. The substrate bonding technique, therefore, has been considered as an effective method for realizing an optoelectronic integrated circuit.
When a device is transferred from one substrate to another substrate by a device manufacturing method such as this, it is important to vertically align the two substrates accurately and determine a position to which the devices are to be transferred. As such a registration method, there has been proposed a method in which registration patterns are checked by means of infrared rays, or a position measuring method in which marks are formed on a substrate and a transparent substrate, respectively, and an image processing technique is employed (Japanese Patent Laid-open Publication No. HEI 3-287321).
The conventional device forming methods, however, have the following disadvantages. First, the registration process becomes complicated and costly when opaque substrates are bonded together since equipments such as an image processing apparatus by means of infrared rays are needed. Secondly, after two substrates have been bonded, a process of removing separation layers by etching takes substantial time.